1. Field of the Invention
The present invention relates to an apparatus and method for cleaning substrates, including semiconductor wafers or other such items requiring extremely high levels of cleanliness.
2. Description of the Related Art
Substrates such as semiconductor wafers are frequently cleaned in a cleaning solution into which megasonic energy is propagated. Megasonic cleaning systems, which operate at a frequency over twenty times higher than ultrasonic, safely and effectively remove particles from materials without the negative side effects associated with ultrasonic cleaning.
One type of megasonic cleaning apparatus shown in U.S. Pat. No. 6,140,744 comprises a piezoelectric transducer coupled to a transmitter in the form of a probe. The transducer is electrically excited such that it vibrates, and the probe transmits high frequency energy into liquid sprayed onto an adjacent, rotating semiconductor wafer. The agitation of the cleaning fluid produced by the megasonic energy loosens particles on the wafer. Contaminants are thus vibrated away from the surfaces of the wafer and removed through the continuous flow of the cleaning fluid.
In U.S. Pat. No. 4,537,511, issued to Frei, an elongated metal tube in a tank of cleaning fluid is energized in the longitudinal wave mode by a transducer that extends through a wall of the tank and is attached to the end of the tube. In order to compensate for relatively high internal losses, the radiating arrangement uses a relatively thin-walled tubular member.
A need exists for an improved apparatus and method which can be used to clean semiconductor wafers and other substrates.